1. Field of the Invention
This invention relates generally to hemodialysis or artificial kidney systems for treatment of blood to remove waste impurities and undesirable components therefrom, and more specifically, to an improved portable hemodialysis system.
2. Description of the Prior Art
Hemodialysis systems have been in general use for a number of years in the treatment of renal disease and disability, and have proven highly effective in providing artificial kidney functions for persons whose own natural kidneys are functionally impaired. In operation of the hemodialysis system, blood containing waste substances, such as for example urea, creatinine, excess electrolytic salts and water, is withdrawn from the body and flowed through a dialyzer in indirect mass transfer relationship with an aqueous dialysate solution. The dialyzer may be of various conventional types including a mass transfer member such as an extended surface elastomeric membrane or a hollow fiber bundle across which the waste substances are transferred by concentration gradient (solute impurities) or osmotic pressure (water) from the blood to the dialysate solution. From the dialyzer the blood which has thus been depleted in impurities is returned to the patient's body. The impurity-enriched dialysate solution from the dialyzer is either disposed of to waste or else is regenerated as by sorbent means to remove the waste impurities therefrom prior to being recirculated to the dialyzer for renewed mass transfer from the blood to the solution.
Although artificial kidney hemodialysis systems have demonstrated widespread acceptance and effectiveness in use, the majority of such systems which have been developed to date are costly, large in size and heavy in weight. Accordingly, these systems have heretofore been primarily employed in hospital renal treatment facilities and "satellite" dialysis centers. The geographically fixed locations of these hemodialysis facilities tends to significantly restrict the mobility of persons requiring dialysis treatment and involves inherent problems of accessibility and expense of travel for persons living in sparsely populated areas or otherwise at a great distance from the treatment center. Due to the widespread character of renal disease and disability, the aforementioned problems affect substantial members of the population; at present, for example, maintenance hemodialysis is employed to preserve and protect the lives of approximately 24,000 persons in the United States alone. One of the greatest limitations of the dialytic regimen of treatment imposed on these patients is a forced alteration in life style as associated with the need for physical attachment to a hemodialysis system two or three times each week.
In an effort to ease the problems of geographical confinement of individual hemodialysis patients, patient travel in groups to areas served by dialysis centers within and outside of the United States has been organized by patient associations such as the National Association of Patients on Hemodialysis and Transplantation (NAPHT). Despite such efforts, however, medical and scheduling problems continue to impede free travel by the dialysis patient. For example, domestic dialysis centers may be filled to capacity and thus unable to accept guest patients. Foreign dialysis centers may be prohibitively expensive or absolutely closed to tourists or visiting patients. In addition, patients who are hepatitus carriers are generally excluded from all centers and thus are denied travel opportunities.
In view of the foregoing problems, considerable effort has been expanded to design and develop low-cost, readily transportable hemodialysis systems. These efforts have not been fully successful for a number of reasons. First, the hemodialysis system requires pumping means to pump blood at sufficient rate through the extracorporeal flow circuit and dialyzer for rapid and efficient mass transfer removal of waste impurities from the blood in the dialyzer. Proper design and selection of the blood pumping device is extremely important, inasmuch as blood is a fragile solution of numerous constituents vital to the patient's metabolic integrity. It is known that blood pumps can cause hemolysis, i.e. damage the cellular elements of blood (red cells, white cells and platelets) as well as denature proteins and lipoproteins. Accordingly, it has been common practice to employ peristaltic roller pumps coupled with a section of flexible resiliant tubing in the extracorporeal blood circuit to pump blood through the flow circuit and dialyzer means. Such pumps typically employ circumferentially spaced apart roller members, mounted on a rotating pump head, which engage and compress the tubing, moving longitudinally along the associated section of tubing to advance blood therethrough and provide pumping capability for the blood flow circuit. These pumps act compressively on the blood flow stream only at or near the points of roller engagement with the resiliant tubing pumping section and thus tend to minimize hemolysis effects. Nonetheless, the peristaltic roller pumps used in hemodialysis systems to date have tended to be large in size, as for example with pump heads measuring 5 to 10 inches in diameter, in order to obtain long pumping segment volumes between the points of contact of the resiliant tubing with adjacent rollers and thereby insure low hemolysis levels while simultaneously pumping blood through the extracorporeal flow circuit at sufficiently high rate to achieve effectively complete dialysis in a suitably short period of time, as for example 4-6 hours.
A second reason that efforts to devise a low-cost, readily transportable hemodialysis system have not been fully successful is that hemodialysis systems typically require extremely large overall volumes of dialysate solution for a total dialysis treatment, e.g., on the order of 100 liters or more. The dialysate solution is an aqueous solution of various selected salts which provide the desired electrolytic balance with the blood in the dialyzer and thus prevent the loss of valuable blood constituents to the dialysate by diffusion and osmosis in the dialyzer. The large volumes of dialysate solution heretofore required for dialysis are associated with reservoir or tankage requirements which are readily accomodated in conventional large-scale hemodialysis systems, but are impractical in application to portable hemodialysis systems. Sorbent regeneration and recirculation of the dialysate solution in the hemodialysis system tends to reduce the volumetric dialysate requirements, but still has problems and requires complex metering pumps to replace salts which are removed during treatment. Proportioning systems have developed for metering and intermixing water from a local source of supply with a comparatively small volume of dialysate solution concentrate. Such systems achieve the portability of a small container of concentrate which, when coupled with a water source by the proportioning means, permits single-pass flow of the dialysate solution through the dialyzer to drain or other waste means, without the necessity of extremely large liquid tankage volumes. Nonetheless, the proportioning systems developed to date have tended to be expensive, bulky and mechanically complex and accordingly have not enjoyed significant application in portable hemodialysis systems.
Accordingly, it is an object of the present invention to provide an improved hemodialysis system for the treatment of blood to remove waste impurities therefrom.
It is also an object of the present invention to provide a hemodialysis system which is compact, lightweight and readily portable.
It is another object of the invention to provide a hemodialysis system with an improved peristaltic roller pump for pumping blood through the extracorporeal blood flow circuit.
It is still another object of the invention to provide an improved hemodialysis system characterized by high dialyzing efficiency which requires a smaller volume of dialysate solution for dialysis than has heretofore been possible.
Other objects and advantages of the invention will be apparent from the ensuing disclosure and appended claims.